Apparatus for post exposure bake of photoresist

ABSTRACT

A method and apparatus for applying an electric field and/or a magnetic field to a photoresist layer without air gap intervention during photolithography processes is provided herein. The method and apparatus include an immersion bake head, which includes an electrode and is configured to be alternated between a hot pedestal and a cold pedestal. The immersion bake head serves as a substrate carrier and applies an electric field to the substrate. The immersion bake head additionally serves to provide and remove process fluid from the substrate using a plurality of fluid conduits.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. provisional patent application Ser. No. 63/149,617, filed Feb. 15, 2021, which is herein incorporated by reference in its entirety. This application further claims benefit of International Application (PCT) serial number PCT/US2022/015146, filed Feb. 3, 2022, which claims priority to each of U.S. non-provisional patent application Ser. No. 17/176,108; U.S. provisional patent application Ser. No. 63/149,617; and U.S. provisional patent application Ser. No. 63/149,618, each filed on Feb. 15, 2021.

BACKGROUND Field

The present disclosure generally relates to methods and apparatus for processing a substrate, and more specifically to methods and apparatus for improving photolithography processes.

Description of the Related Art

Integrated circuits have evolved into complex devices that can include millions of components (e.g., transistors, capacitors and resistors) on a single chip. Photolithography is a process that may be used to form components on a chip. Generally the process of photolithography involves a few basic stages. Initially, a photoresist layer is formed on a substrate. A chemically amplified photoresist may include a resist resin and a photoacid generator. The photoacid generator, upon exposure to electromagnetic radiation in the subsequent exposure stage, alters the solubility of the photoresist in the development process. The electromagnetic radiation may have any suitable wavelength, for example, a 193 nm ArF laser, an electron beam, an ion beam, or other suitable source.

In an exposure stage, a photomask or reticle may be used to selectively expose certain regions of the substrate to electromagnetic radiation. Other exposure methods may be maskless exposure methods. Exposure to light may decompose the photo acid generator, which generates acid and results in a latent acid image in the resist resin. After exposure, the substrate may be heated in a post-exposure bake process. During the post-exposure bake process, the acid generated by the photoacid generator reacts with the resist resin, changing the solubility of the resist during the subsequent development process.

After the post-exposure bake, the substrate, particularly the photoresist layer, is developed and rinsed. Depending on the type of photoresist used, regions of the substrate that were exposed to electromagnetic radiation are either resistant to removal or more prone to removal. After development and rinsing, the pattern of the mask is transferred to the substrate using a wet or dry etch process.

The evolution of chip design continually requires faster circuitry and greater circuit density. The demands for greater circuit density necessitate a reduction in the dimensions of the integrated circuit components. As the dimensions of the integrated circuit components are reduced, more elements are required to be placed in a given area on a semiconductor integrated circuit. Accordingly, the lithography process must transfer even smaller features onto a substrate, and lithography must do so precisely, accurately, and without damage. In order to precisely and accurately transfer features onto a substrate, high resolution lithography may use a light source that provides radiation at small wavelengths. Small wavelengths help to reduce the minimum printable size on a substrate or wafer. However, small wavelength lithography suffers from problems, such as low throughput, increased line edge roughness, and/or decreased resist sensitivity.

An electrode assembly may be utilized to generate an electric field to a photoresist layer disposed on the substrate prior to or after an exposure process so as to modify chemical properties of a portion of the photoresist layer where the electromagnetic radiation is transmitted for improving lithography exposure/development resolution. However, the challenges in implementing such systems have not yet been adequately overcome.

Therefore, there is a need for improved methods and apparatus for improving immersion field guided post exposure bake processes.

SUMMARY

The present disclosure generally relates to substrate process apparatus. Specifically, embodiments of the disclosure relate to an immersion bake head assembly. The immersion bake head assembly includes a head body and a support surface disposed on a lower surface of the head body. One or more first fluid conduits are disposed through the head body with one or more first openings in fluid communication with a central region of the support surface. One or more second fluid conduits are disposed through the head body with one or more second openings in fluid communication with an outer region of the support surface. A permeable electrode is coupled to the support surface.

In another embodiment, an immersion bake head assembly includes a head body and a support surface disposed on a lower surface of the head body. One or more fluid inlet conduits are disposed through the head body with one or more fluid inlet openings in fluid communication with a central region of the support surface. One or more fluid removal conduits are disposed through the head body with one or more fluid removal openings in fluid communication with an outer region of the support surface. A permeable electrode is coupled to the support surface and overlaps the one or more fluid inlet openings and the one or more fluid removal openings. The permeable electrode is a conductive material with a resistivity of less than about 5×10⁻⁴ Ω·m.

In yet another embodiment, an immersion field guided post exposure bake module includes an immersion bake head assembly, a cooling pedestal, and a heating pedestal. The immersion bake head assembly includes a head body, a support surface disposed on a lower surface of the head body, one or more first fluid conduits disposed through the head body with one or more first openings in fluid communication with a central region of the support surface, one or more second fluid conduits disposed through the head body with one or more second openings in fluid communication with an outer region of the support surface, and a permeable electrode coupled to the support surface. The cooling pedestal includes one or more cooling elements disposed therein. The heating pedestal includes one or more heating elements disposed therein.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments and are therefore not to be considered limiting of its scope, may admit to other equally effective embodiments.

FIG. 1 is a schematic plan view of an immersion field guided post exposure bake module according to embodiments described herein.

FIG. 2A is a schematic cross-sectional view of an immersion bake head disposed over a cooling pedestal within the immersion field guided post exposure bake module of FIG. 1, according to embodiments described herein.

FIGS. 2B-2C are schematic cross-sectional views of an immersion bake head disposed over a heating pedestal within the immersion field guided post exposure bake module of FIG. 1, according to embodiments described herein.

FIG. 3 illustrates operations of a method for performing an immersion post exposure bake process according to an embodiment described herein.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

DETAILED DESCRIPTION

The present disclosure generally relates to methods and apparatus for post exposure bake processes. Methods and apparatus disclosed herein assist in reducing line edge/width roughness and improving exposure resolution in a photolithography process for semiconductor application.

The methods and apparatus disclosed herein improve the photoresist sensitivity and productivity of photolithography processes. The random diffusion of charged species generated by a photoacid generator during a post exposure bake procedure contributes to line edge/width roughness and reduced resist sensitivity. An electrode assembly, such as those described herein, is utilized to apply an electric field and/or a magnetic field to the photoresist layer during photolithography processes. The field application controls the diffusion of the charged species generated by the photoacid generator. Furthermore, an intermediate medium is utilized between the photoresist layer and the electrode assembly so as to enhance the electric field generated therebetween.

An air gap defined between the photoresist layer and the electrode assembly results in voltage drop applied to the electrode assembly, thus, adversely lowering the level of the electric field desired to be generated to the photoresist layer. Inaccurate levels of the electric field at the photoresist layer may result in insufficient or inaccurate voltage power to drive or create charged species in the photoresist layer in certain desired directions, thus leading to diminished line edge profile control to the photoresist layer. Thus, an intermediate medium is placed between the photoresist layer and the electrode assembly to prevent an air gap from being created therebetween so as to maintain the level of the electric field interacting with the photoresist layer at a certain desired level. By doing so, the charged species generated by the electric field are guided in a desired direction along the line and spacing direction, substantially preventing the line edge/width roughness that results from inaccurate and random diffusion. Thus, a controlled or desired level of electric field as generated increases the accuracy and sensitivity of the photoresist layer to expose and/or development processes. In one example, the intermediate medium is a non-gas phase medium, such as a slurry, gel, liquid solution, or a solid state medium that may efficiently maintain voltage levels as applied at a determined range when transmitting from the electrode assembly to the photoresist layer disposed on the substrate.

Even while using the intermediate medium, a voltage drop is still present between the photoresist layer and the electrode assembly. This voltage drop is directly related to the distance between the photoresist layer and the electrode assembly. Therefore, reducing the distance between the photoresist layer and the electrode assembly assists in improving the uniformity of the electric field between the photoresist layer and the electrode assembly. Another consideration while using the intermediate medium is bubbling between the photoresist layer and the electrode assembly. Bubbling and the formation of air pockets between the photoresist layer and the electrode assembly cause non-uniformities within the electric field and therefore increases the number of defects and inaccuracies within the photoresist after the post-exposure bake process. The present apparatus and methods described herein for reducing the distance between the photoresist and the electrode assembly beneficially reduce the number of bubbles or air pockets between the photoresist layer and the electrode assembly.

FIG. 1 is a schematic plan view of an immersion field guided post exposure bake module 100 according to embodiments described herein. The immersion field guided post exposure bake module 100 includes a module body 102, a cooling pedestal 110 disposed within the module body 102, a heating pedestal 120 disposed within the module body 102, and an immersion bake head 106 disposed within the module body 102. Each of the cooling pedestal 110, the heating pedestal 120, and the immersion bake head 106 are disposed within a module volume 130, which is defined by the module body 102.

The immersion bake head 106 is an immersion field guided post exposure bake head. The immersion bake head 106 is configured to pick up a substrate from the cooling pedestal 110, transfer the substrate to the heating pedestal 120, and provide an electric field to the substrate while the substrate is disposed on the heating pedestal 120. The substrate is held in place by a combination of clamping and surface tension between the substrate and a process fluid supplied by the immersion bake head 106.

A substrate transfer passage 104 is disposed through a wall of the module body 102. The substrate transfer passage 104 is configured to allow a substrate to pass therethrough. The substrate transfer passage 104 is horizontally elongated to allow substrates to pass through the passage 104 in a horizontal orientation. The substrate transfer passage 104 connects the module volume 130 with an outside volume of another module or process chamber. The substrate transfer passage 104 is disposed adjacent to the cooling pedestal 110, as the substrate is configured to be picked up from the cooling pedestal 110. The substrate transfer passage 104 is closer to the cooling pedestal 110 than the heating pedestal 120. The substrate transfer passage 104 is coupled with a valve (not shown) for opening and closing the substrate transfer passage 104.

The immersion bake head 106 is transferred between the cooling pedestal 110 and the heating pedestal 120 by a transfer arm 150. The transfer arm 150 is coupled to the immersion bake head 106 and includes an actuating base 112 and an arm 108. The arm 108 connects the actuating base 112 and the immersion bake head 106. The actuating base 112 is disposed between the cooling pedestal 110 and the heating pedestal 120. The actuating base 112 is a rotary actuator and swings the immersion bake head 106 between a position above the cooling pedestal 110 and the heating pedestal 120 between process operations. In some embodiments, there may be additional heating pedestals 120 and cooling pedestals 110 within the module body 102 along with multiple immersion bake heads 106 and transfer arms 150.

The immersion bake head 106 is coupled to a control panel 140. The control panel 140 is described in greater detail below, but includes a combination of gas panels, fluid panels, controllers, and power sources. In some embodiments, there is not a single control panel 140, but the control panel 140 is instead representative of a plurality of gas panels, fluid panels, controllers, and power sources. The control panel 140 is coupled to the transfer arm 150, such that fluid and power lines pass through the arm 108 to supply fluids and power to the immersion bake head 106.

FIG. 2A is a schematic cross-sectional view of an immersion bake head 106 disposed over a cooling pedestal 110 within the immersion field guided post exposure bake module 100 of FIG. 1, according to embodiments described herein. The immersion bake head 106 is shown in a position for picking up or releasing a substrate, such as the substrate 250, from the cooling pedestal 110. The immersion bake head 106 is configured to be lowered towards the substrate 250 before gripping the substrate 250 using one or a combination of surface tension and a clamp.

The immersion bake head 106 includes a head body 210, a support surface 256 disposed on a lower surface 221 of the head body 210. One or more first fluid conduits 214 are disposed through the head body 210 in fluid communication with a central region R₁ of the support surface 256. One or more second fluid conduits 212 are disposed through the head body 210 at an outer region R₂ of the support surface 256. An electrode 218 is coupled to the support surface 256.

The support surface 256 is a portion of the lower surface 221 of the head body 210. The support surface 256 is a planar portion of the lower surface 221 and is disposed within the head body 210 and offset from other portions of the lower surface 221 in some embodiments. The support surface 256 is sized to allow a substrate, such as the substrate 250 to be disposed thereon, such that the support surface 256 has a diameter of greater than about 200 mm, such as greater than about 250 mm, such as greater than about 300 mm. The head body 210 is formed of an insulated material, such as a ceramic. In some embodiments, the head body 210 is formed of a material with a resistivity of greater than about 10×10¹⁹ Ω·m, such as greater than about 10×10²⁰ Ω·m. In some embodiments, the head body 210 is formed of a polytetrafluoroethylene (PTFE), a fluoropolymer material, Teflon, polyether ether ketone (PEEK), or Al₂O₃.

The one or more first fluid conduits 214 are disposed through the head body 210 and are configured to provide process fluid to the top surface of the substrate 250. The one or more first fluid conduits 214 are one or more fluid inlet conduits. The one or more first fluid conduits 214 are shown as a single fluid conduit with a fluid inlet opening 213 disposed in the support surface 256. The one or more first fluid conduits 214 are fluidly coupled to a process fluid supply 206. The process fluid supply 206 supplies process fluid to the one or more first fluid conduits 214 and therefore to a processing volume 252 in some embodiments is described as a fluid volume or a process fluid volume. The process fluid is an intermediate medium used to improve the uniformity of the electric field between the electrode 218 and the substrate 250 during post exposure bake operations. The process fluid is a non-gas phase medium, such as a slurry, gel, liquid solution, or a solid state medium that efficiently maintain voltage levels as applied at a determined range when transmitting from the electrode assembly to the photoresist layer disposed on the substrate.

The fluid inlet opening 213 is disposed adjacent to the electrode 218 and is configured to provide process fluid to the central region R₁. The central region R₁ is defined as the inner 30 mm of the support surface 256 of the head body 210, such that the central region R₁ is a disk with a radius of 15 mm. The central region R₁ corresponds to about the center 30 mm of the substrate 250.

The one or more second fluid conduits 212 are disposed through the head body 210 and are configured to remove process fluid from the processing volume 252 and the top surface of the substrate 250. The one or more second fluid conduits 212 are one or more fluid removal conduits. The one or more second fluid conduits 212 are shown as two mirrored fluid conduits with a fluid removal opening 215 disposed in the support surface 256. The one or more second fluid conduits 212 are fluidly coupled to a fluid removal pump 202. The fluid removal pump 202 removes process fluid from the processing volume 252 through the one or more second fluid conduits 212. In some embodiments, the one or more second fluid conduits 212 are a single conduit or are a single conduit which splits into a plurality of conduits.

The fluid removal opening 215 is an annular opening, which is disposed in the support surface 256. The fluid removal opening 215 is disposed adjacent to a portion of the electrode 218 and is configured to remove process fluid from the outer region R₂. The outer region R₂ is defined as the outer 35 mm of the support surface 256 of the head body 210, such that the outer region R₂ is an annular ring with a thickness of about 25 mm. The outer region R₂ is disposed about 125 mm to about 150 mm from the center of the support surface 256. The outer region R₂ corresponds to about the outer 25 mm of the substrate 250. The fluid removal opening 215 is disposed radially outward of the fluid inlet opening 213, such that the fluid removal opening 215 removes process fluid near the edge of the substrate 250, while the fluid inlet opening 213 supplied process fluid to the center of the substrate 250. In some embodiments, the one or more fluid removal openings 215 are arcuate or circular openings disposed within the support surface, such that the annular opening is broken in sections to form a plurality of arcs with a same center of curvature and a same radii.

The electrode 218 is coupled to the support surface 256 and includes a planar bottom surface 254. The electrode 218 is permeable to allow fluid to pass therethrough, for example through perforations, mesh, pores, or other fluid permeable structures. The electrode 218 includes a plurality of fine openings disposed therethrough to allow either gas, process fluid, or both gas and process fluid to pass therethrough. In some embodiments, the electrode 218 is a conductive mesh. The electrode 218 is utilized in order to reduce the amount of bubbles or gas pockets, which are trapped under the electrode assembly support surface 256 as the electrode 218 is submerged into the process fluid. The electrode 218 in some embodiments, is a non-metal mesh, such as a silicon carbide mesh, such as a doped silicon carbide. In other embodiments, the electrode 218 is a conductive metal mesh, such as a copper, aluminum, platinum, or a steel mesh. The electrode 218 is formed of a material which has an electrical resistivity of less than about 5×10⁻⁴ Ω·m, such as less than 5×10⁻⁵ Ω·m, such as less than 5×10⁻⁶ Ω·m. The electrode 218 is electrically coupled to an electrode power source 204. The electrode power source 204 is configured to apply power to the electrode 218. In some embodiments, an electrical potential of up to 5000 V is applied to the electrode 218 by the electrode power source 204, such as less than 4000 V, such as less than 3000 V.

Each of the electrode power source 204, the fluid removal pump 202, and the process fluid supply 206 are disposed as part of the control panel 140. The control panel 140 controls the flow rates of the fluid removal pump 202 and the process fluid supply 206. The control panel 140 additionally controls the voltage applied by the electrode power source 204.

One or more clamps 216 are disposed on the lower surface 221 of the head body 210. The one or more clamps 216 are shown herein as mechanical clamps, such that the clamps 216 move between an opened and a closed position. The clamps 216 are in an open position when not in contact with the substrate 250 and are in a closed position when contacting the bottom surface of the substrate 250. The one or more clamps 216 are attached to the head body 210 radially outward of the electrode 218 and the support surface 256. The one or more clamps 216 are configured to clamp an edge of the substrate 250 to assist in supporting the substrate 250 during the post-exposure bake operations. The clamps 216 may also be vacuum clamps. Mechanical clamps are used herein as mechanical clamping may clamp either the side or bottom surface of the substrate 250 and a greater amount of the top surface of the substrate 250 is able to be submerged in the process fluid and undergo a post-exposure bake operation. There are three or more clamps 216 when using a mechanical clamp.

The cooling pedestal 110 includes a pedestal body 222, a substrate cooling support surface 264 disposed on top of the pedestal body 222, a plurality of lift pins 226, and one or more cooling elements 230. The substrate cooling support surface 264 is a planar surface meant to receive a substrate 250 and support the substrate 250 between process operations. The immersion bake head 106 picks up the substrate 250 from the substrate cooling support surface 264. In some embodiments, the substrate cooling support surface 264 has a slightly smaller diameter than the substrate 250 to allow the clamps 216 to grip the substrate 250. The cooling pedestal 110 is a highly conductive material, with an electrical resistivity of less than about 1×10⁻³ Ω·m, such as less than 1×10⁻⁴ Ω·m, such as less than 1×10⁻⁵ Ω·m. The contact resistance between the cooling pedestal 110 and the substrate 250 has a greater impact on the ability of the cooling pedestal 110 to electrically ground the substrate 250 than the resistivity of the cooling pedestal 110 itself. In embodiments described herein, the contact resistance between the cooling pedestal 110 and the substrate 250 is less than about 1×10⁻³Ω, such as less than about 1×10⁻⁴Ω. In some embodiments, the cooling pedestal 110 is an aluminum, a doped silicon carbide, or a dopes silicon material.

The lift pins 226 are disposed through the pedestal body 222 and are configured to lift and lower the substrate 250, such that a robot arm or indexer (not shown) may remove the substrate 250 from the module body 102. The lift pins 226 are disposed within lift pin holes 224 of the pedestal body 222. The lift pin holes 224 are cylindrical holes disposed through the pedestal body 222. There are three lift pin holes 224 total.

The one or more cooling elements 230 disposed through the pedestal body 222 are cooling fluid conduits. The cooling fluid conduits are cooling pipes disposed through the pedestal. The one or more cooling elements 230 are coupled to a coolant source 232 by a coolant supply line 220. The coolant source 232 may supply water or another coolant fluid to the pedestal body 222.

The cooling pedestal 110 is grounded by a ground line 208. Grounding the cooling pedestal 110 assists in providing a voltage differential between the electrode 218 and the substrate 250.

FIGS. 2B-2C are schematic cross-sectional views of an immersion bake head 106 disposed over a heating pedestal 120 within the immersion field guided post exposure bake module 100 of FIG. 1, according to embodiments described herein. The heating pedestal 120 includes a pedestal body 223 with one or more heating elements 266 disposed therein.

The one or more heating elements 266 may be resistive heating elements, heated pipes, or a lamp assembly. As shown in FIGS. 2B and 2C, the one or more heating elements 266 are resistive heating elements. The one or more heating elements are coupled to a heating power source 258 by a power line 227. The heating elements 266 are configured to raise the temperature of the substrate 250 to a temperature of about 80° C. to about 250° C., such as about 90° C. to about 230° C., such as about 90° C. to about 130° C.

The heating pedestal 120 is a highly conductive material, with an electrical resistivity of less than about 1×10⁻³ Ω·m, such as less than 1×10⁻⁴ Ω·m, such as less than 1×10⁻⁵ Ω·m. The contact resistance between the heating pedestal 120 and the substrate 250 has a greater impact on the ability of the heating pedestal 120 to electrically ground the substrate 250 than the resistivity of the heating pedestal 120 itself. In embodiments described herein, the contact resistance between the heating pedestal 120 and the substrate 250 is less than about 1×10⁻³Ω, such as less than about 1×10⁻⁴Ω. In some embodiments, the heating pedestal 120 is an aluminum, a doped silicon carbide, or a dopes silicon material. The heating pedestal 120 is grounded by a ground line 208 similar to the ground line of the cooling pedestal 110.

A top surface 262 of the pedestal body 222 is configured to receive a substrate, such as the substrate 250. The top surface 262 is planar and is a substrate receiving surface. The top surface 262 is configured to contact the substrate 250 and ground the substrate 250 during application of an electric field.

FIG. 2B illustrates the substrate 250 while gripped by the immersion bake head 106 and before placing the substrate 250 onto the heating pedestal 120. The substrate 250 is gripped by the one or more clamps 216 and the surface tension of a process fluid volume 260. As shown, the process fluid flows out from the one or more first fluid conduits 214, out over the top surface of the substrate 250, and is removed via the one or more second fluid conduits 212. The process fluid may flow through the electrode 218. In some embodiments, the surface tension of the process fluid within the process fluid volume 260 may hold the substrate 250 without the use of additional clamps 216.

FIG. 2C illustrates the substrate 250 coupled to the immersion bake head 106, but also placed on top of the top surface 262 of the pedestal body 222 of the heating pedestal 120. Placing the substrate 250 on top of the heating pedestal 120 enables the rapid heating of the substrate 250 on a pre-heated pedestal. While the substrate 250 is coupled to the immersion bake head 106, the top surface of the substrate 250 is a height H from the bottom surface of the electrode 218. The height H is less than about 4 mm, such as less than about 3 mm, such as less than about 2 mm, such as less than about 1 mm. The height H is smaller to improve the uniformity of the electric field applied to the substrate 250. Apparatus described herein enable smaller distances between the electrode 218 and the substrate 250 as the location and size of fluid transfer passages do not limit the distance between the two surfaces and the substrate 250 is processed by the same apparatus which transfers and secures the substrate 250. Reducing the distance between the electrode 218 and the substrate 250 further enables the reduction of a voltage difference between the substrate 250 and the electrode 218 used to create an electric field.

FIG. 3 illustrates operations of a method 300 for performing an immersion post exposure bake process according to an embodiment described herein. The method 300 includes a first operation 302 of loading a substrate, such as the substrate 250, onto a first pedestal, such as the cooling pedestal 110. Loading the substrate onto the first pedestal includes passing the substrate through a substrate transfer passage, such as the substrate transfer passage 104. The substrate is positioned on the first pedestal by a robot (not shown). The first pedestal is configured to cool the substrate. After positioning the substrate onto the first pedestal, an immersion bake head, such as the immersion bake head 106, is lowered towards the substrate to a pick-up position during a second operation 304. The pick up position includes the immersion bake head being disposed directly above the substrate and within 2 mm of the substrate, such as less than 1 mm from the substrate, such as less than 0.5 mm from the substrate, such as less than 0.25 mm from the substrate. After the second operation 304, a third operation 30 is performed to fill a fluid volume with a process fluid. The process fluid is an intermediate medium. The intermediate medium is a non-gas phase medium, such as a slurry, gel, liquid solution, or a solid state medium that may efficiently maintain voltage levels as applied at a determined range when transmitting from the electrode assembly to the photoresist layer disposed on the substrate.

Either simultaneously with or immediately after the third operation 306, the substrate is secured to the immersion bake head during a fourth operation 308. Securing the substrate is performed using one or more clamps, such as the clamps 216. The clamps are moved to a closed position to secure an edge of the substrate. In some embodiments, the bottom edge of the substrate is clamped to provide support to the substrate. In some embodiments, by filling the fluid volume with the process fluid, the substrate is gripped by the process fluid and a surface tension force. The surface tension force in some embodiments, is great enough to hold the substrate in place while lifting the substrate and transferring between different locations.

After the fourth operation 308, the substrate is transferred to a second pedestal during a fifth operation 310. The second pedestal is a heating pedestal, such as the heating pedestal 120. The substrate is transferred to the second pedestal by the immersion bake head apparatus. Transferring the substrate includes lifting the substrate from the first pedestal, moving the substrate to above a second pedestal, and lowering the substrate to contact the second pedestal. As the second pedestal is a heating pedestal, the substrate is then heated during a sixth operation 312. During the sixth operation 312, the substrate is heated to a temperature of about 80° C. to about 250° C., such as about 90° C. to about 230° C., such as about 90° C. to about 130° C. The rapid increase in temperature assists in the post exposure bake process. In embodiments described herein, the second pedestal is pre-heated and the temperature of the substrate is able to be rapidly increased since the substrate is placed on a pre-heated substrate.

After and/or during heating the substrate during the sixth operation 312, an electric field is applied to the substrate using an electrode, such as the electrode 218, during a seventh operation 314. The electrode is additionally coupled to the immersion bake head and is configured to perform a post exposure bake process thereon. The electric field is applied by applying an electric potential of up to 5000 V to the electrode by an electrode power source, such as less than 4000 V, such as less than 3000 V. In embodiments described herein, the reduced distance between the substrate and the electrode enabled by the apparatus herein greatly reduces the electric potential used for processing of the substrate. In some embodiments, an electric potential of less than 1000 V is applied to the electrode, such as less than 500 V, such as less than 250 V, such as less than 100 V, such as less than 10 V. The electric potential utilized to form the electric field is at least partially dependent upon the gap size between the electrode and the substrate. An electric field between the electrode and the substrate is less than about 1×10⁷ V/m, such as less than 1×10⁶ V/m, such as less than 1×10⁵V/m. The electric field may be about 1×10⁵ V/m to about 1×10⁷ V/m, such as about 1×10⁵ V/m to about 1×10⁶ V/m. The strength of the electric field is limited by the breakdown voltage of the medium disposed within the process volume. In some embodiments, the breakdown voltage of the fluid disposed within the process volume is about 1.4×10⁷ V/m. In some embodiments, the electric field is between about 10×10⁶ V/m and about 1×10⁴ V/m. The electric field is applied to the substrate until the post exposure bake operation is complete.

After applying the electric field during the seventh operation 314, the substrate is transferred back to the first pedestal during an eighth operation 316. Transferring the substrate back to the first pedestal includes lifting the substrate from the second pedestal using the immersion bake head, moving the substrate to above the first pedestal, and lowering the substrate to contact an upper surface of the first pedestal.

After placing the substrate onto the first pedestal, the substrate is released from the immersion bake head during a ninth operation 318. Releasing the immersion bake head includes stopping the flow of process fluid to the substrate from a central process fluid supply opening. The process fluid will be removed by outer process fluid supply openings and decouples from the immersion bake head. Any clamps may also be disengaged to release the substrate. The immersion bake head may then be moved upwards and away from the substrate to an intermediate position. After the substrate is placed on the first pedestal, the substrate is removed from the first pedestal during a tenth operation 320. The tenth operation 320 is similar to the first operation 302, but in reverse and includes moving the lift pins and removing the substrate using an indexer or robot arm.

Embodiments described herein are beneficial in that substrates may be inserted into the process station apparatus while in a horizontal position. The process stations herein also reduce bubbling effects on the post exposure bake process and allow for the electrodes and substrate to be disposed closer together during processing, which reduces the impact of electric field non-uniformities. Using the surface tension of the process fluid at least partially supports the substrate. Utilizing the surface tension disposed between the electrode and the substrate further reduces the distance between the electrode and substrate improves the post-exposure bake process reliability and performance. Reducing the distance between the electrode and the substrate further reduces the voltage provided to the electrode to enable a suitable electric field strength. Using alternating hot and cold pedestals also beneficially allows the substrate to be rapidly heated by being placed on a pre-heated pedestal. As overheating often causes overbaking of the substrate, embodiments described herein assist in reducing overbaking of substrates processed therein.

While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow. 

What is claimed is:
 1. An immersion bake head assembly, comprising: a head body; a support surface disposed on a lower surface of the head body; one or more first fluid conduits disposed through the head body with one or more first openings in fluid communication with a central region of the support surface; one or more second fluid conduits disposed through the head body with one or more second openings in fluid communication with an outer region of the support surface; and a permeable electrode coupled to the support surface.
 2. The immersion bake head assembly of claim 1, further comprising a clamp coupled to a lower surface of the head body.
 3. The immersion bake head assembly of claim 2, wherein the clamp is a mechanical clamp.
 4. The immersion bake head assembly of claim 1, wherein the head body is coupled to a transfer arm.
 5. The immersion bake head assembly of claim 1, wherein the permeable electrode is a conductive mesh.
 6. The immersion bake head assembly of claim 1, wherein the permeable electrode is a conductive material with a resistivity of less than about 5×10⁻⁴ Ω·m.
 7. The immersion bake head assembly of claim 6, wherein the conductive material is one or a combination of copper, aluminum, platinum, steel, or a doped silicon carbide.
 8. An immersion bake head assembly, comprising: a head body; a support surface disposed on a lower surface of the head body; one or more fluid inlets conduits disposed through the head body with one or more fluid inlet openings in fluid communication with a central region of the support surface; one or more fluid removal conduits disposed through the head body with one or more fluid removal openings in fluid communication with an outer region of the support surface; and a permeable electrode coupled to the support surface and overlapping the one or more fluid inlet openings and the one or more fluid removal openings, wherein the permeable electrode is a conductive material with a resistivity of less than about 5×10⁻⁴ Ω·m.
 9. The immersion bake head assembly of claim 8, wherein the outer region of the support surface is an annular ring disposed around the central region of the support surface.
 10. The immersion bake head assembly of claim 8, further comprising a clamp coupled to a lower surface of the head body.
 11. The immersion bake head assembly of claim 10, wherein the clamp is a mechanical clamp.
 12. The immersion bake head assembly of claim 8, wherein the one or more fluid removal openings are arcuate or circular openings disposed within the support surface.
 13. The immersion bake head assembly of claim 8, wherein the head body is an insulating material with a resistivity of greater than about 10×10¹⁹ Ω·m.
 14. An immersion field guided post exposure bake module, comprising: an immersion bake head assembly comprising: a head body; a support surface disposed on a lower surface of the head body; one or more first fluid conduits disposed through the head body with one or more first openings in fluid communication with a central region of the support surface; one or more second fluid conduits disposed through the head body with one or more second openings in fluid communication with an outer region of the support surface; and a permeable electrode coupled to the support surface; a cooling pedestal with one or more cooling elements disposed therein; and a heating pedestal with one or more heating elements disposed therein.
 15. The immersion field guided post exposure bake module of claim 14, wherein the one or more cooling elements comprise one or more cooling channels disposed therein.
 16. The immersion field guided post exposure bake module of claim 15, wherein the cooling pedestal further includes a plurality of lift pins disposed therein.
 17. The immersion field guided post exposure bake module of claim 14, wherein the one or more heating elements comprise a plurality of resistive heating elements.
 18. The immersion field guided post exposure bake module of claim 14, wherein the permeable electrode overlaps the one or more fluid inlet openings and the one or more fluid removal openings.
 19. The immersion field guided post exposure bake module of claim 14, wherein the permeable electrode is a conductive mesh.
 20. The immersion field guided post exposure bake module of claim 14, wherein the head body is coupled to a transfer arm. 